Avro 720
The Avro 720 was a planned British single-seat interceptor of the 1950s. It was to be of mixed propulsion, with a rocket engine to give high performance and a small jet engine for cruising flight. At least one prototype was ordered, but the project was cancelled before any were completed. Design and development In the early 1950s, the British Air Ministry, impressed by the performance of the rocket-powered Messerschmitt Me 163 fighter, and facing the potential threat of Soviet supersonic bombers armed with nuclear weapons, issued Specification F.124T for a rocket-powered point-defence interceptor. This was to be of similar concept to the Me 163, using its rocket to climb rapidly to meet its target, before gliding back to earth, fuel exhausted, to land on a retractable skid. Proposals to meet the specification were received from a number of companies, including Avro, Bristol, Blackburn, Shorts and Saunders-Roe. It was soon realised, however, that a rocket-only fighter with the performance required by the specification, which would have to glide back to ground from heights of up to 100,000 ft (30,500 m), land without power many miles away and then be recovered and taken back to the airfield by ground vehicle, was impracticable. Revised specifications were therefore issued to Avro and Saunders-Roe for aircraft with auxiliary turbojet engines, giving sufficient power to allow the aircraft to fly back to its airbase after combat.Jones Aeroplane Monthly November 1994, pp. 32–33.Mason 1992, p. 400. Avro's design, the Avro Type 720, designed to meet specification F.173D, was a small tailless delta-winged aircraft. It was constructed of metal honeycomb sandwich. The main power-plant was an 8,000 lbf (36 kN) Armstrong Siddeley Screamer rocket engine, using liquid oxygen as oxidant and kerosine fuel. This differed from the competing Saunders-Roe SR.53, which used a de Havilland Spectre powered by Hydrogen Peroxide and kerosine. Both types used a 1,750 lbf (7.8 kN) Armstrong-Siddeley Viper as the auxiliary turbojet, with the Avro design fed with air from a small chin inlet under the aircraft's nose. Two de Havilland Firestreak Infrared homing air-to-air missiles could be carried on underwing pylons. Two prototypes were ordered, and the Screamer engine successfully completed flight clearance tests in December 1956.Flight 27 July 1956, p. 164. Official concern about the practicality of using liquid oxygen, which boils at -183 °C (90 K), in an operational environment led to the Screamer engine being cancelled late in 1956, together with the Avro 720.Flight 24 May 1957, pp. 698–699. One structural test airframe was part complete at the time of cancellation, and photographs of this airframe, with the port wing fitted and the serial number XD696 painted on are sometimes claimed to be the "almost complete" first prototype. The Avro 720 had cost £1 Million by the time of cancellation, while its Screamer powerplant cost a further £0.65 million.Flight 17 August 1967, p. 262. Specifications (Performance estimated) See also *Republic XF-91 Thunderceptor *Saunders-Roe SR.53 *SNCASO Trident *List of aircraft of the Royal Air Force References ;Notes ;Bibliography * "Armstrong Siddeley Screamer". Flight, 27 July 1956. pp. 160–164. * "Cancelled Projects:The list Up-Dated". Flight, 17 August 1967, p. 262. * Jackson, A. J. Avro Aircraft since 1908. London:Putnam, 1990. ISBN 0-85177-834-8. * Jones, Barry. "Saro's Mixed-Power Saga". Aeroplane Monthly, November 1994. London:IPC. ISSN 0143-7240. pp. 32–39. * Mason, Francis K. The British Fighter since 1912. Annapolis, Maryland, USA:Naval Institute Press, 1992. ISBN 1-55750-082-7. * "Mixed-Power Interceptor". Flight, 24 May 1957, pp. 697–700. Category:Cancelled military aircraft projects of the United Kingdom 720 Category:1950s British fighter aircraft Category:Mixed-power aircraft Category:Rocket-powered aircraft